Magnetic chuck attachment plate



Junll, 1946." F. SHEPPARD MAGNETIC CHUCK ATTACHMENT PLATE Filed Aug. 10,1944 A/O/V-MlG/VET/C M5741 I I I I l I Patented June 1 1, 1946 MAGNETICCHUCK ATTACHMENT PLATE Frank Sheppard, Greenfield Park, Quebec,

Canad Application August 10, 1944, Serial No. 548,860 In Canada August30, 1943 The present invention relates to magnetic chucks and, moreparticularly, an attachment therefor adapted to hold very small partstobe machined.

Magnetic chucks are well-known devices adapted to hold, by magnetism,ferrous and other magnetic metallic parts for machining and otherpurposes. Said chucks generally consist of spaced poles, oppositelymagnetized by means of an inner electric coil, and the upper surface ofwhich is perfectly flat and smooth.

Inasmuch as the poles and polar gaps are relatively large in saidchucks, for reasons of electrical design, they are not very well adaptedt hold metallic pieces smaller than the space between said poles.

The present invention has been conceived to avoid the disadvantage notedabove, in a simple device adapting an average chuck to the use of smallparts.

The main object of the invention, therefore, resides in the provision ofmeans for rendering a magnetic chuck operative to retain small parts inan efficient manner.

Another object of the invention is the provision of means of thecharacter noted, which means are simple, inexpensive and operable byanyone.

A further object contemplates means of the character described which areinstantly adaptable to conventional chucks without adjustments oralterations thereto.

Other objects and advantages of the invention will become apparent, orbe further pointed out, during the description to follow.

As an example, and for purposes of illustration, two forms of theinvention are shown in the annexed drawing wherein:

Figure 1 is a perspective view of the preferred form of the invention ifplaced over a magnetic chuck,

Figure 2 is a vertical longitudinal section through the device of theinvention shown in Figure 1,

Figure 3 is a perspective View of a modified form of the invention, and

Figure 4 -is a longitudinal vertical section through said modified form.

Referring to the drawing, wherein similar reference characters representcorresponding parts throughout, the letter C generally indicates amagnetic chuck of conventional design, said chuck having inter-leavedpoles P of opposite polarity, said poles being energized, as usual, byan inner magnetic coil (not shown). As previously stated, the spacing ofthe poles is such as 5 Claims. (Cl. 367) 2 to preclude the possibilityof holding small objects because, as is well known, the retaining powerof the chuck is directly proportional to the number of pairs of opposedpolarity pole bridged by the object to be retained.

Consequently, in order to concentrate the magnetic flux emanating fromthe pole P into a more concentrated magnetic field, the device of theinvention has been conceived, which device is indicated generally by theletter A.

The said device is in the form of a composite plate adapted to be useddirectly on the face of a magnetic chuck, as shown in Figure 1.

Said plate A consists essentially of a number of ferrous metal taperedsegments 5, separated by non-magnetic metal strips 6, the said stripsand segments being soldered together, bolted or, as shown, retainedtogether by means of dowels l of non-magnetic metal and press-fittedlongitudinally on the mass constituting the plate A.

As shown to advantage in Figures 1 and 2, the segments and strips are sodisposed that they converge toward a common center or foca1 point whichis theoretically disposed above the plate. The purpose of thisarrangement is to space the segments, by means of the strips, so thatsaid segments have a lower case approximately of a Width correspondingsubstantially to the physical dimensions of the usual magnetic chuckwith which it is desired to be associated. Furthermore, the taperedformation permits the said segments to be closer together at the top,whereby the magnetic field, or flux, conveyed from the poles P throughthe segments 5, appears on top of the plate A as a concentrated magneticfield better adapted to hold small objects which, due to the closeproximity of the poles, can bridge a number thereof for better and moreeflicient holding facilities.

Obviously, after the plate has been roughly assembled, the upper andlower surfaces thereof are perfectly levelled. and rendered parallel.The flux is completed by the addition of end triangular pieces l0adapted to act as retaining members for the dowels l or other means usedfor joining the elements of the plate in place.

From the foregoing description, and with the aid of Figure 1, it will beobvious that the plate A, disposed as shown, permits the small part Pengaged by the grinding wheel G to bridge, in effect, at least five ofthe poles of the magnetic chuck C. Obviously, without the intermediaryof said plate A, the physical dimensions of P would be such as to hardlybridge more than two poles of the chuck C with correspondingly reducedholding power.

A modified form of the invention is shown in Figure 3, which form isvery substantially the same as that shown in Figure 1, with theexception that one-half only of plate A is actually used. Morespecifically, the modified plate B embodies a central segment II theouter surface of which is perfectly perpendicular to the base of theplate and has to the right of said segment a number of similar segmentsI2 spaced by the strips I3 as previously disclosed. In this form also,one end piece I4 only is provided which may act as a slot to which theretaining members l5 are secured in any suitable manner.

The specific purpose of the modified form is to hold a small metallicpart M on the very edge of the plate B so that the grinding wheel G mayhave access to the side edges of said part M for specific purposes. Asection of this modified form is shown in Figure 4 which, as a matter offact, is substantially the preferred form of Figure 1 cut in half andwith the central nonmagnetic metal strips 6 removed.

The uses to which the device can be put are believed to be fairlyobvious from the illustrations, it being necessary simply to place theplate over a magnetic flux in a manner such that the base of thesegments corresponds as closely as possible with the poles of the chuck.Of course, it may occur, in certain cases, that the alignment is notperfect due to physical difierences in size, but the great number ofmagnetic lines conveyed to the small parts by means of the segments isusually sufl'lcient to hold the same in perfect position for machining,grinding or hand working.

In practice, the plate A should have a certain thickness for providing amass sufi'lcient to react to the strain imposed by the magnetic flux.The number of converging mild iron segments is sufficiently limited toavoid lengthening the magnetic path unduly, whereby the end segments arerendered less eflicient. Besides, since the attachment of the inventionis provided solely for retaining small parts, it is evident that itsphysical dimensions can be kept relatively small.

It must be understood that various changes as to the shape, size andarrangement of parts can be efiectuated without departing from thespirit of the invention or the scope of the subjoined claims.

Having thus described my invention, I claim:

1. A device of the character described, comprising a plurality of spacednon-magnetic strips, said strips converging towards a common centerpoint, and segmental magnetic members interposed between said strips,the assembly having top and bottom surfaces at right angles to the planeof the central magnetic strip.

2. As an attachment to magnetic chucks, a rectangular composite platehaving bottom and top plane faces, triangular end pieces, a plurality ofalternating magnetic and non-magnetic members disposed between said endpieces, said members converging to a common focal point above the top,and means between the end pieces for clamping said members.

3. A plate of the character described, comprising a plurality ofalternate magnetic and non-magnetic members, the magnetic memberstapering from the bottom to the top thereof, whereby a plate is obtainedhaving narrow magnetic areas at the top and wide magnetic areas at thebottom.

4. An attachment of the character described, comprising magnetic andnon-magnetic elements in juxtaposed alternative positions, and means forsecuring said elements in close contact, the said elements beingarranged radially around a common theoretical center, with thenon-magnetic elements of uniform thickness and the magnetic one taperingfrom the bottom to the top thereof.

5. As an article of manufacture, a magnetic chuck attachment comprisinga plate or rectangular shape having top and bottom plane surfaces, saidplate consisting of magnetic and nonmagnetic elements inclinedvertically towards the center of said plate, whereby the magneticelements are narrower at the top than at the bottom for the purpose ofholding small parts securely.

FRANK SHEPPARD.

